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Evidence for a developmentally regulated prespore-specific glutamine synthetase in the cellular slime mould
Andrew J Dunbar1, John F Wheldrake1
1School of Biological Sciences, The Flinders University of South Australia, Bedford Park, GPO Box 2100, Adelaide 5001, Australia.
Abstract:
The enzyme glutamine synthetase (GS) is described for the first time in Dictyostelium discoideum. The appearance of this enzyme is developmentally regulated. The level of activity is low in vegetative cells and increases more than threefold during differentiation. Furthermore this enzyme is shown to be differentially localized in prespore cells, the specific activity being approximately fourfold higher than in prestalk cells. The enzyme has a pH optimum of 7.8 and 8.2 in the gamma-glutamyltransferase and gamma-glutamylsynthetase assays, respectively, and a temperature optimum of 45 degrees C. Kinetic studies of GS revealed apparent Km values of 5.9 mM, 0.009 mM and 8.6 mM for glutamine, ADP and NH2OH, respectively, in the gamma-glutamyltransferase assay, and of 2.2 mM, 0.12 mM and 0.64 mM for glutamate, ATP and NH2OH, respectively, in the gamma-glutamylsynthetase assay.
